1. Field of the Invention
This invention relates to circuit breakers and, more particularly, to remotely controlled circuit breakers having one or both of ground fault and arc fault trip mechanisms.
2. Background Information
Circuit breakers are generally old and well known in the art. Examples of circuit breakers are disclosed in U.S. Pat. Nos. 5,260,676; and 5,293,522. Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition.
In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, circuit protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which is heated and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. In one circuit breaker, for example, the thermal characteristic responds to 30 A being drawn in a 15 A circuit. On the other hand, an armature, which is attracted by the sizable magnetic forces generated in a magnetic core by a short circuit or fault, also unlatches, or trips, the operating mechanism. As an example, the magnetic type actuation occurs when the hot line conductor becomes directly connected with ground or neutral, thereby bypassing the load.
It is known to provide a remotely controlled circuit breaker wherein the separable contacts are tripped to an open condition by an actuator responding to a control signal.
It is further known to provide a remotely controlled circuit breaker having main separable contacts and also having auxiliary or switching relay separable contacts which are opened by an actuator responding to a control signal. This enables the circuit breaker to additionally perform a switching function and manage a load connected to the breaker, such that the breaker performs the dual functions of overload current protection and load management.
In many applications, a miniature circuit breaker may provide ground fault protection. Typically, an electronic circuit detects leakage of current to ground and generates a ground fault trip signal. This trip signal energizes a shunt trip solenoid, which unlatches the operating mechanism, typically through actuation of the thermal-magnetic trip device.
A common type of ground fault detection circuit is the dormant oscillator detector including first and second sensor coils. The line and neutral conductors of the protected circuit pass through the first sensor coil. The output of this coil is applied through a coupling capacitor to an operational amplifier followed by a window comparator having two reference values. A line-to-ground fault causes the magnitude of the amplified signal to exceed the magnitude of the reference values and, thus, generates a trip signal. At least the neutral conductor of the protected circuit passes through the second sensor coil. A neutral-to-ground fault couples the two detector coils which causes the amplifier to oscillate, thereby resulting in the generation of the trip signal. See, for example, U.S. Pat. Nos. 5,260,676; and 5,293,522.
Recently, there has been considerable interest in also providing protection against arc faults. Arc faults are intermittent high impedance faults which can be caused, for instance, by worn insulation between adjacent conductors, by exposed ends between broken conductors, by faulty connections, and in other situations where conducting elements are in close proximity. Because of their intermittent and high impedance nature, arc faults do not generate currents of either sufficient instantaneous magnitude or sufficient average RMS current to trip the conventional circuit breaker. Even so, the arcs can cause damage or start a fire if they occur near combustible material. It is not practical to simply lower the pick-up currents on conventional circuit breakers, as there are many typical loads, which draw similar currents and would, therefore, cause nuisance trips. Consequently, separate electrical circuits have been developed for generating an arc fault trip signal to respond to arc faults. See, for example, U.S. Pat. Nos. 5,224,006; and 5,691,869. The arc fault trip signal energizes a shunt trip solenoid, which unlatches the operating mechanism, typically through actuation of the thermal-magnetic trip device.
Although the prior art shows a wide range of circuit breakers, there is room for improvement.
The invention is directed to a circuit breaker including first separable contacts, second separable contacts in series with the first separable contacts, and one or both of means for detecting a ground fault and means for detecting an arc fault. An actuator means is energizable by one or both of the means for detecting a ground fault and the means for detecting an arc fault. Absent arc fault and ground fault conditions, the first separable contacts are normally opened in response to predetermined current conditions, while the second separable contacts are normally opened in response to a signal. Otherwise, an actuator means is energizable by one or both of the means for detecting a ground fault and the means for detecting an arc fault to open the second separable contacts.
A circuit breaker in accordance with the invention includes first separable contacts, and means for opening the first separable contacts in response to predetermined current conditions. The circuit breaker further includes second separable contacts in series with the first separable contacts, and means for operating the second separable contacts in response to a signal. The circuit breaker also includes at least one of: (a) means for detecting a ground fault, and (b) means for detecting an arc fault. An actuator means, energizable by such at least one of the means for detecting a ground fault and the means for detecting an arc fault, actuates the means for operating the second separable contacts to open the second separable contacts. In this manner, following a ground fault or an arc fault, a signal, such as a remote external signal, may be employed to reset the circuit breaker after a ground fault or arc fault without requiring local manual intervention.
Preferably, the actuator means is a solenoid means for actuating the means for operating the second separable contacts.